I will bet that there is not anyone here on this list that comes anywhere near the time that I have spent with these engines at high load values . Time spent on the track and in the dyno.
In my business I do not change anything unless there is good data to support the change .
If it is not broken dont try to fix it .

The only difference in the gates belt and the stock one is that the gates belt does not stretch much , it settles and than that is it , I have changed both my engines to it and both use the stock tensioner , all of the parts carry over from second hand engines and measures to ensure specification .
My biggest critisism of the new arrangement is no alarm , this allows the slack on the belt or non correct tension to be unmonitored . It is common for the stock belt to be in specification and give a warning during a bgt rev. So I leant early that for track work it is needing to be set up accordingly at the high end of the tolling scale (not over tensioned ) . the gates belt not so much .

In 4 years of track work and hundreds of hours of dyno time with the stock system, no problems and no maintenance (ie no replacement parts only inspection) . Bearing in mind the GT engine was rebuilt 3 times due bearing issues , until a solution was found . (that another story) (both engines use GBs scavenge head system with other parts that I included race car is dry sumped )
THe stock system will also have the belt slip if the alarm system is non functional . How do I know ?
Due to my own error I had the belt slip 15 teeth on my new track engine in the dyno luckily not under full load, due to the tensioner not set properly ( my fault) . In this case I avoided the clash of pistons and valves as the engine backfired and shut down immediately , causing my heart to skip a few beats . As my units have all after market engine management (Adaptronic Racetech dash) the coding logic that I had created for the cam belt alarm didnt work in the way that I expected too again my fault .
As I have stated previously you all need to see one of these engines run under high and varying load and watch how the cam belt appears like a rubber band , that is why some sort of tension alarm is mandated. not having one is hoping the problem does not exist eg ostrich syndrome .
As someone else had stated this system is not like other units , it is the longest production belt in history , so the factory spent probably thousands of hours in develoment.
I am not stating that the pkt is good bad or indifferent only my own experience in 30 years . we also should be mindful of not hindering the developmen tof additional parts supplier for the same.

 

And adjusted it properly. And readjusted it.


You have yet to answer these questions, Big Deal:

 

I personally think both sides that have been arguing need to chill out a bit on this one. The OP (who I really feel for) already admitted that he failed to follow instructions on the excessive piston extension which ultimately led to this failure. Errors can be made on installation of both systems that can lead to different types of failure. I have made colossal errors working on my 928, I learned and moved forward. Both tensioners have their positive and negative points and we can beat it to death all day long and get nowhere.

Maybe Ken can use this data to help find a way to make improvements to his product. To say the stock system is good enough, well it was 25 years ago. If it was the end all be all Porsche would use a belt and manual tensioner on their new V8 engines but they don't. There has to be a way to make it better, and if nobody supports change then nothing gets done.

 

I have. Which is why I pimp the PKT. If you were to see this with a PKT, you would be happy to see no noodling on the slack side. The belt is always absolutely flat.

Depending on different resonances at different rpm you will see skittering between the other gears, but the slack side will always be flat.

What looks the weirdest to me is at high rpm, the belt is so much heavier it extends flat out from the water pump longer and longer before it heads to the 5-8 gear.

 

I may have missed some, how many instances of engine damage has so far occurred to 928s with the PK Tensioner system?

 

See below.

 

To be precise - one. A hardware issue as Ken states.
There was another possible failure - not totally proven - on a race engine. As all bets are off when it comes to race engines and race performance I do not consider this in the reckoning. No damage to the engine as it was a none interference engine. If it ever was researched it would have been a hardware issue and already covered by the PKT "Black" system.

As far as this issue is concerned the jury is still out until I see cold hard facts and not propaganda from both sides. I do feel for Erik of course.

Worth noting is that the only documented failure - due to a hardware issue - was replaced by a PKT and NOT THE OLD SYSTEM.

All PKT users - and there are hundreds of them - choose the system themselves based on the merits that they see. When I quote I always show the alternative of rebuilding the old de-tensioning system v the modern automatic PKT system. On cost alone the PKT proves a better option. I am and will always be a firm believer in the PKT system and have it fitted to all my cars.

As a 928 owner I would never use the old system "just because it works". Far happier to use more modern technology and I for one am glad we have extremely clever people out there like Ken who took the time to develop products like his. This goes for GB as well as all the other clever designers/engineers/developers.

And before you say I make money selling the PKT system and business wise I am biased, bear in mind that I can make more money selling the old system.

Occasionally any engineered system will have a problem at some point - just a fact of life. Without progress and new designs we will not get very far.

 

Fwiw I have had PKT on my high miles daily driver 88 S4 for a few years now, which gets driven through all seasons, winter, summer and it has been through a low, and then dead battery. Regular gates belt. No issues so far and engine is nice and smooth at all rpms.
I just ordered another PKT from Roger for my other 87 S4 to replace the stock system.

Back in the 90s I had an issue with an intermittent tensioner light on the stock system. A reputable Porsche shop I used couldn't figure it out and would tighten the belt. The water pump failed not long after. I shut the engine off as temps rose. All was good though. This is the same car I drive now. While the stock setup had a warning, it did me no good because the failing pump was not detected despite several visits to the shop. It would be nice to have a warning system with PKT, but in my case the result would have either been the same, rising temps and turn off engine, ...or maybe the pump would not have failed as early. Who knows.

 

Ken:

Not really my job to provide you with data or tell you what I do when I assemble my own engines....I'm sure everyone can understand that.

Besides that, I'm sure my data would just be a duplication of what you learned while "inventing" your Portensioner.

To everyone else:

I've got nothing else to add here. Ken calling me names isn't answering questions or working towards solving the problem at hand. Try to get my questions answered by Ken....hopefully you will have better luck than I have....all I get is smart a$$ responces and snide comments.

And always remember....any failure of the stock tensioner isn't going to ruin your engine.

I'm out of this thread.

 

Are you saying the belt wasn't loose for a while before the valves got bent?

 

I'm making no assertions at all, save that we need more data. It's possible that it was.

 

The tensioner type is the least important bit of the matrix. The belt and rollers play a far more important role in the belt tracking/slipping issue. And I admitted I never installed a Pkensioner, but maybe you missed that prev post.

 

Agreed. The stock tension warning system has a 3 min lockout where it is defeated from annuciation possibly due to the time allowed for the engine to grow into it's belt torque range. The OP was cranking a cold engine, the stock warning system would not be activated yet.

 

If the stock tensioner fails in a way that it no longer retracts when the block heats up and expands thermally, it will over tension the belt and may lead to worn cam gears and seized water pump. Both can lead to catastrophic damage to the block and the heads.

On planet Earth where humans and not robots operate these machines, the belt tension warning light however has caused more damage to these cars than any other design flaw. Malfunctioning tensioner warning leads humans to over tighten the belt and causing the water pump to seize, cam gears to wear, cams to break, etc. The addition of that warning light was pretty much the dumbest thing to do, considering that the intended users were humans.

Despite the name calling and spreading of FUD, I think this thread has been useful in forcing me to think some issues thru. For example, it's now logically clear to me that the racing belt should be installed and used just the same way as the stock belt.

The two open questions that I still have are the following:

(1) if using stiffer valve springs and the stock tensioner, how much higher should the belt pre-tension be set and how to calibrate that whole process?

(2) how does the PKT system respond to all the various crank and cam angles that the engine can stop when the engine is not running, and how that question should impact the installed depth of the PKT hydraulic tensioner?

 

Greg is right to a point, the stock tensioner does not cause severe damage when it fails, but all that other stuff touching the tensioner does. The rollers, the bolt, the bushings, all do though. Whose to say that this car would have not had a problem with the stock set up? From what I can see this issue has zero to do with the PKT as the failure is somewhere else.

But what do I know.